Materials analysis using X-rays provides accurate data in a number of applications and industries. X-ray fluorescence (XRF) measurements allow the determination of the elemental composition of a sample. This may be carried out in dedicated X-ray fluorescence apparatus with an X-ray source, an X-ray detector and a sample stage for holding a sample.
In order to make an XRF measurement it is necessary to measure the intensity of X-rays at a particular wavelength, equivalently energy, excited in a sample by the incident X-ray beam. In the case of energy dispersive XRF, an energy dispersive detector is used, i.e. a detector that measures the X-ray intensity as a function of energy. However, for high accuracy, especially where the emission lines of different elements are close in energy and even overlapping, this approach may not provide enough energy resolution. In this case, in an alternative approach, wavelength selective XRF is used. In this alternative approach, a wavelength selecting crystal is provided between the sample stage and the X-ray detector to select only a particular wavelength for measurement by the X-ray detector.
High accuracy XRF apparatus typically mount the wavelength selecting crystal and X-ray detector on a goniometer to allow the wavelength selecting crystal and X-ray detector to be moved to different positions to select different wavelengths. Where it is necessary to measure a sample with multiple components, each component is measured in turn before realigning the wavelength selecting crystal and X-ray detector for the next measurement.
The length of time to make a measurement of a single component varies as a result of a number of factors, including how much of a component is present in a sample and the desired accuracy. However, in general, it may be said that accurately measuring a large number of components in a sample may take a considerable time, especially where some of the components are trace components present in small quantities.
This time taken for measurement can be a particular concern in some industrial applications. For example, where the XRF measurement is intended to check the composition of steel, it may be necessary to pause the production process while the measurement is being made before releasing the molten metal to the next stage of a process. This can cost a considerable amount of resource in maintaining the temperature above the melting temperature. Similarly, in a mining application, it may again be necessary to evaluate the material being extracted from the earth rapidly.
In an existing solution to this problem, a large number of different X-ray detectors are each used, each aligned with a fixed wavelength selecting crystal to measure a particular wavelength and hence a particular element. This allows measurements to be made in parallel. However, such equipment is not suitable in cost-sensitive applications since there is a need for a large number of X-ray components.
Energy dispersive XRF measures X-ray intensity as a function of energy and measures a number of elements simultaneously. Its performance is very good for transition metals. For low atomic number its sensitivity is poor compared to WDS. For the high energy of high atomic number elements the efficiency of the detector is low for thin Si body detectors (˜500 um), the X-rays may pass through the detector with little interaction, so energy dispersive XRF may also be unsuitable at very high energies.
There therefore remains a need for speeding up the measurement of the composition of a sample using XRF.